Browntop invasion into hill country sown to ryegrass-white clover showed rapid vegetative spread over 2 years followed by dense tiller development. Initially a distribution mosaic formed, ryegrass and clover being positively associated with each other, but negatively associated with browntop. Subsequently, 'browntop spread into the ryegrass-clover microsites. Browntop ingressed under close, continuous grazing but not under lax, rotational grazing. Competitive interactions of clover and 'Grasslands Ruanui' and 'Grasslands Manawa' ryegrasses ,involved were partitioned. Browntop was markedly suppressed by interspecific shading under infrequent cutting, but survived to spread into spaces provided by nonpersistent ryegrass. Management to modify competition for light to control browntop is considered.